在几个GEV重离子碰撞中测量λ超子的全局极化

论文标题

在几个GEV重离子碰撞中测量λ超子的全局极化

Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisions

论文作者

Yassine, R. Abou, Adamczewski-Musch, J., Asal, C., Becker, M., Belounnas, A., Blanco, A., Blume, C., Chlad, L., Chudoba, P., Ciepal, I., Cordts, M., Dreyer, J., Esmail, W. A., Fabbietti, L., Floersheimer, H., Fonte, P., Friese, J., Fröhlich, I., Förtsch, J., Galatyuk, T., Gniazdowski, T, Greifenhagen, R., Grunwald, M., Gumberidze, M., Harabasz, S., Heinz, T., Höhne, C., Hojeij, F., Holzmann, R., Huck, H., Idzik, M., Kämpfer, B., Kampert, K-H., Kardan, B., Kedych, V., Koenig, I., Koenig, W., Kohls, M., Kolas, J., Kornakov, G., Kotte, R., Kres, I., Krueger, W., Kugler, A., Lalik, R., Lebedev, S., Linev, S., Linz, F., Lopes, L., Lorenz, M., Malige, A., Markert, J., Matulewicz, T., Maurus, S., Metag, V., Michel, J., Molenda, A., Müntz, C., Nabroth, M., Naumann, L., Nowakowski, K., Orliński, J., Otto, J. -H., Parschau, M., Pauly, C., Pechenov, V., Pechenova, O., Pfeifer, D., Piasecki, K., Pietraszko, J., Povar, T., Prozorov, A., Przygoda, W., Pysz, K., Ramstein, B., Rathod, N., Ritman, J., Rodriguez-Ramos, P., Rost, A., Rustamov, A., Salabura, P., Saraiva, J., Schild, N., Schwab, E., Scozzi, F., Seck, F., Selyuzhenkov, I., Singh, U., Skorpil, L., Smyrski, J., Spies, S., Stefaniak, M. S., Ströbele, H., Stroth, J., Sumara, K., Svoboda, O., Szala, M., Tlusty, P., Traxler, M., Wagner, V., Wasiluk, M., Weber, A. A., Wendisch, C., Wirth, J., Zbroszczyk, H. P., Zherebtsova, E., Zielinski, M., Zumbruch, P.

论文摘要

根据\ sqrt {s_ {nn}} = 2.4 Gev和Ag+ag的高统计数据样本，沿相对论重型离子碰撞的总眶角动量的全局极化是根据高统计数据样本= 2.4 Gev和Ag+ag，高高的gev gev和ag ag ags coll-ectermon atmectron at arterm at arterm at arterm and arterm（这是核子核子碰撞中陌生产生阈值以下的第一个测量。报告的结果是碰撞中心性的函数以及超子横向动量（P_T）和速度（y_ {cm}）的函数0--40％的范围。我们观察到极化的强度依赖性，而信号越来越对周围碰撞。对于中央中部（20--40％）碰撞，极化幅度为<p_λ>（％）= 6.8 \ pm 1.3（stat。）\ pm 2.1（syst。）对于Au+AU和<p_λ>（％）= 6.2 \ pm 0.4（stat。因此，该观察结果可延续以前观察到的趋势的不断增长，并从最近的理论计算中对比预期，预测碰撞能量的最大值约为3 GEV。观察到的极化与3D流体动力学和URQMD和热涡度模型所预测的相似大小，并且显着高于AMPT模型的结果。

The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au collisions at \sqrt{s_{NN}} = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality 0--40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20--40%) collisions the polarization magnitudes are <P_Λ>(%) = 6.8 \pm 1.3 (stat.) \pm 2.1 (syst.) for Au+Au and <P_Λ>(%) = 6.2 \pm 0.4 (stat.) \pm 0.6 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D fluid dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.

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